Preheat oven to 350°F (175°C). Lightly grease a muffin tin with oil spray.
In a large bowl, whisk together mochiko, granulated sugar, brown sugar, baking powder, and salt until well combined.
In a separate bowl, whisk together the eggs, coconut milk, melted butter, black sesame paste, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients. Whisk until fully combined and smooth.
Divide the batter evenly into the prepared muffin tin.
Bake for 30–40 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs.
Allow muffins to cool in the tin for 10 minutes, then transfer to a wire rack to cool completely.